Strained semiconductor device and method of making same

ABSTRACT

In a method of making a semiconductor device, a gate dielectric is formed over the semiconductor body. A floating gate is formed over the gate dielectric, an insulating region over the floating gate, and a control gate over the insulating region. The gate dielectric, floating gate, insulating region, and control gate constitute a gate stack. A stress is caused in the gate stack, whereby the band gap of the gate dielectric is changed by the stress.

This application is a divisional of U.S. patent application Ser. No.11/546,662, entitled “Strained Semiconductor Device and Method of MakingSame,” filed on Oct. 12, 2006 now U.S. Pat. No. 7,651,915, whichapplication is incorporated herein by reference.

TECHNICAL FIELD

This invention relates generally to semiconductor devices and methods,and more particularly to devices and methods for modulating stress intransistors in order to improve performance.

BACKGROUND

Semiconductor devices are used in a large number of electronic devices,such as computers, cell phones and others. One of the goals of thesemiconductor industry is to continue shrinking the size and increasingthe speed of individual devices. Smaller devices can operate at higherspeeds since the physical gate length is smaller and follows theuniversal scaling law. In addition, higher conductivity materials, suchas copper, are replacing lower conductivity materials, such as aluminum.As the geometries of semiconductor devices shrink and their performanceimproves, however, the maintaining low leakage current becomes achallenge.

One type of semiconductor device is a memory device, in which data istypically stored as a logical “1” or “0.” Memory devices may be staticor dynamic. Dynamic memory devices need to be refreshed to “remember”the data, whereas static memory devices do not need to be refreshed toretain stored data.

One type of static memory device, also referred to in the art as anon-volatile memory (NVM) device, is a flash memory device. A flashmemory device is an electrically erasable programmable read only memory(EEPROM) that is commonly used in computers, digital cameras, MP3players, gaming systems, and memory sticks, as examples, although flashmemory devices may be used in other applications, as well. Flash memorydevices do not require power to retain stored data; they retain dataeven when the power source is disconnected. In flash memory devices,in-circuit wiring is used to erase predetermined sections or blocks ofthe chip by applying an electrical field to the entire chip, forexample.

Flash memory devices typically comprise an array of flash memory cells.Flash memory cells are accessible for programming and retrieving data byan array of wordlines and bitlines coupled to the array of flash memorycells. Each flash memory cell comprises a floating gate and a controlgate, which are separated by a thin insulator. Flash memory cells areprogrammed by applying a voltage to the control gate. Flash memory cellsstore a charge in the floating gate and are programmed usingFowler-Nordheim tunneling or channel hot electron injection from thechannel or source and drain regions.

Recent flash memory applications include “embedded flash memory” andsystem on a chip (SoC) devices, in which an array of flash memory cellsand peripheral circuitry for the flash memory cells are formed togetherwith the microcontroller or processor on a single chip or integratedcircuit. The peripheral circuitry may comprise high voltage circuits,for column/row decoders or drivers, charge pumps, transfer gates orother logic circuits for microcontrollers or processors, and other typesof devices that may comprise transistors, diodes, bandgap devices,capacitors, inductors, and linear devices, as examples, although othertypes of devices may be included in the peripheral circuitry.

In the field of non-volatile memories (NVM), it is very desirable toshrink the size of the NVM cell so that either more memory can be storedin a given area to achieve higher density, or a given amount of memorytakes up less silicon area to achieve more die per wafer to furtherreduce costs. Scaling down the size of the NVM cell requires reducingthe length of the gate. This is typically achieved by thinning thetunnel oxide to control the short channel effect. A thinner tunneloxide, however, leads to increased leakage current and loss of thestored charge on the floating gate. This negatively impacts the chargeretention lifetime and the device reliability. What is needed is amethod to prevent leakage current in NVMs while allowing for a reducedNVM cell size to take advantage of shrinking geometries.

SUMMARY OF THE INVENTION

In a method of making a semiconductor device, a gate dielectric isformed over the semiconductor body. A floating gate is formed over thegate dielectric, an insulating region over the floating gate, and acontrol gate over the insulating region. The gate dielectric, floatinggate, insulating region, and control gate constitute a gate stack. Astress to the gate is caused in the gate dielectric, whereby an energygap of the gate dielectric is changed by the stress.

The foregoing has outlined rather broadly features of the presentinvention. Additional features of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present invention. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1 a-1 e provide cross-sectional views and a flowchart of a firstembodiment process;

FIGS. 2 a-2 d provide cross-sectional views and a flowchart of a secondembodiment process;

FIGS. 3 a-3 d provide cross-sectional views and a flowchart of a thirdembodiment process;

Corresponding numerals and symbols in different figures generally referto corresponding parts unless otherwise indicated. The figures are drawnto clearly illustrate the relevant aspects of the preferred embodimentsand are not necessarily drawn to scale. To more clearly illustratecertain embodiments, a letter indicating variations of the samestructure, material, or process step may follow a figure number.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of preferred embodiments are discussed in detailbelow. It should be appreciated, however, that the present inventionprovides many applicable inventive concepts that may be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the invention,and do not limit the scope of the invention.

The invention will now be described with respect to preferredembodiments in a specific context, namely a method for reducing leakagecurrent in a floating gate NVM device. Concepts of the invention canalso be applied, however, to other electronic devices. For example,other classes of non-volatile memories, such as single poly chargetrapping devices, devices which replace the floating polysilicon gate byONO or high K dielectrics, SONOS, MONOS, and NROM. Other devices, suchas volatile memories, transistors and other logic devices, can alsoutilize concepts of the invention.

Strained silicon can be used to improve the mobility of the channel ofan MOS device. Various aspects of the present invention utilize strainin a transistor device, such as a floating gate transistor, to increasethe energy gap of the gate dielectric. A device with a high energy gapis prone to less leakage. It has been discovered that in standard finegeometry devices, stress does not have a large impact on the energy gapbecause of the difficulty of introducing stress into a very thin oxide.In NVM devices, where the tunnel oxide is thicker, the introduction ofstress to the gate has a more significant impact on the energy gap.Introducing stress in the gate of an NVM device is challenging, however,because of the difficulty of delivering enough stress to the gate areain order to adequately improve performance.

Various methods for the formation of transistor devices using theseconcepts will be described with respect to FIGS. 1 a-1 e, FIGS. 2 a-2 d,and FIGS. 3 a-3 d.

In the first embodiment of the present invention, stress is introducedinto the gate area by depositing a stress liner over a partially formedtransistor. In order to increase the level of stress in the transistor,however, one of the spacers in the process is removed prior to thedeposition of the stress liner.

FIGS. 1 a-1 d illustrate cross-sectional views of various steps inimplementing the first embodiment. FIG. 1 e provides a flow diagram thatdescribes the fabrication steps for the first embodiment. The stepsdenoted with a “*” in FIG. 1 e are steps which are used for thefabrication of NVM and high voltage devices. The remaining steps areused for low voltage devices or are common to all devices in theprocess.

An initial structure, which is produced from steps 150 to 194 in FIG. 1e, is shown in FIG. 1 a. A semiconductor body 104 is shown, on top ofwhich two devices, an NVM device 100 and a standard MOS device 102(e.g., an NMOS or PMOS transistor), are fabricated. For the NVM device,a tunnel oxide layer 106, a floating gate 108, an insulating layer 110,a control gate 112, and a silicide layer 118 are formed over thesemiconductor body 104. For the standard device 102, a gate dielectriclayer 114, a gate electrode 116, and a silicide layer 118 are formedover the semiconductor body 104. A first spacer 120 is formed at thesidewalls and extension area of the NVM device and on the sidewalls andextension areas of the standard device. A second spacer 122 is formed onthe first spacer. Layers 112 and 116 typically share the same gatematerials.

Looking to the process flow shown in FIG. 1 e, in a preferred embodimentCMOS NVM process a starting wafer is provided (block 150) and shallowtrench isolation regions (STI) are formed in the semiconductor body(block 152). First, isolation trenches can be formed using conventionaltechniques. For example, a hard mask layer, such as silicon nitride, canbe formed over the semiconductor body and patterned to expose theisolation areas. The exposed portions of the semiconductor body can thenbe etched to the appropriate depth.

The trenches are then filled with an isolating material. For example,exposed silicon surfaces can be thermally oxidized to form a thin oxidelayer. The trenches can then be lined with a first material such as anitride layer (e.g., Si₃N₄). The trenches can then be filled with asecond material, such as an oxide. For example, a high density plasma(HDP) can be performed, with the resulting fill material being referredto as HDP oxide. In other embodiments, other trench filling processescan be used.

In step 154, the HV triple wells are formed using conventionaltechniques. In the present embodiment process, n-wells are created forthe PMOS devices, p-wells are created for the NMOS devices, and triplewells are formed for the NMOS NVM devices. In other embodiments,modified triple wells could be used for the logic transistors and/or theNVM devices could be formed in a single (or double well) in which PMOSNVM are formed on n-wells over N-substrate.

The flash memory tunnel oxide is formed in step 156 using hightemperature thermal process. In the first embodiment of the presentinvention, the tunnel oxide layer 106 preferably comprises an oxide,such as silicon dioxide or SiON, although the thin tunnel oxide 106 mayalternatively comprise high k dielectric materials, such as Al₂O₃ orHfSiON, combinations or multiple layers thereof, or combinations ormultiple layers thereof with silicon dioxide, as examples, althoughother materials may also be used. The tunnel oxide layer 106 preferablycomprises a thickness of about 10 nm or less as an example, although thetunnel oxide layer 106 may alternatively comprise other thicknesses.

In step 158, the floating gate is formed. In the preferred embodiment ofthe present invention, the floating gate 108 preferably comprises about150 nm or less of polysilicon that is in-situ low doped, e.g., withn-type dopants, for an n-channel flash memory device. Alternatively, thefloating gate 108 may comprise other materials and/or may be in-situ lowdoped with p-type dopants, for example, for a p-channel flash memorydevice, and the floating gate 108 may comprise other thicknesses. Thepolysilicon is deposited using LPCVD in a furnace while being exposed tophosphine gas for n-type doping. The floating gate polysilicon istypically doped to a concentration of between 5×10¹⁸ cm⁻³ and 1×10²⁰cm⁻³. Alternatively, floating gate 108 may comprise an ONO or high Kdielectric such as HfSiO2, HfSiON, Al₂O₃, or other materials as insingle poly charge trapping devices.

A floating gate slot etch which serves to define columns of NVM deviceparallel to bitline direction, is performed in step 160 using photoresist and a reactive ion etch (RIE). In the preferred embodiment, thefloating gate 108 is etched using a dry etch. In some embodiments, thetunnel oxide is also etched, but care must be taken not to damage theoxide through plasma etch or create a recess in the surroundingsemiconductor body 104.

In step 163, the NVM device's insulating dielectric 110 is formed overthe floating gate 108 and preferably comprises a tri-layer ofoxide/nitride/oxide (ONO). Alternatively, the insulating layer 110 maycomprise a high k dielectric material such as HfSiO₂, HfSiON, Al₂O₃, orother materials. In one embodiment, the insulating layer 110 maycomprise a first layer comprising a low temperature polysilicon oxide, asecond layer comprising a low pressure chemical vapor deposition (LPCVD)nitride disposed over the first layer, and a third layer comprising ahigh temperature oxide disposed over the second layer. For example, thefirst layer may be formed by thermal oxidation of the semiconductordevice 100 to about 900° C., and exposing the floating gate 108 tooxygen; the second layer may be formed by depositing silicon nitrideusing LPCVD, and the third layer may be formed by heating thesemiconductor device 100 in the presence of steam to oxidize the secondlayer at a temperature of about 900° C., and/or depositing oxide orre-oxidizing the second layer of nitride to form silicon dioxide. Theinsulating dielectric 110 preferably comprises an equivalent oxidethickness of about 20 nm to about 12 nm.

The ONO is patterned and etched in using photoresist in step 164. In apreferred embodiment, the ONO is also etched away from all non-NVMdevices, such as the high voltage and standard logic devices.

The preferred embodiment includes high voltage devices, e.g., chargepumps or decoders or drivers as well as transfer gate transistors thatmust withstand higher voltages. In step 166, the high voltage gate oxideis formed, e.g., by thermal oxidation, patterned and etched in usingphotoresist in step 167. In step 168, the LV wells are formed usingconventional techniques.

In step 170, the control gate 112 is formed by a dedicated NVM gatemask. A gate dielectric layer 114 (also deposited on top of dielectriclayer 110) is formed over a portion of a semiconductor body 104. In oneembodiment, the gate dielectric 114 comprises a thermally grown RTOoxide (e.g., SiO₂), or combination of oxide and nitride (e.g., SiON,oxynitrided-oxide sequence). In other embodiments, a high-k dielectricmaterial having a dielectric constant of about 5.0 or greater is used asthe gate dielectric 114. Suitable high-k materials include HfO₂,HfSiO_(x), Al₂O₃, ZrO₂, ZrSiO_(X), Ta₂O₅, La₂O₃, nitrides thereof,HfAlO_(x), HfAlO_(x)N_(1-x-y), ZrAlO_(x), ZrAlO_(x)N_(y), SiAlO_(x),SiAlO_(x)N_(1-x-y), HfSiAlO_(x), HfSiAlO_(x)N_(y), ZrSiAlO_(x),ZrSiAlO_(x)N_(y), combinations thereof, or combinations thereof withSiO₂, as examples. Alternatively, the gate dielectric 114 can compriseother high-k insulating materials or other dielectric materials. Asimplied above, the gate dielectric 114 may comprise a single layer ofmaterial, or alternatively, the gate dielectric 114 may comprise two ormore layers.

The gate dielectric 114 may be deposited by chemical vapor deposition(CVD), atomic layer deposition (ALD), metal organic chemical vapordeposition (MOCVD), or jet vapor deposition (JVD), as examples. In otherembodiments, the gate dielectric 114 may be deposited using othersuitable deposition techniques. The gate dielectric 114 preferablycomprises a thickness of about 8-16 Å to about 60 Å in one embodiment,although alternatively, the gate dielectric 114 may comprise otherdimensions.

A gate electrode layer 112/116 is formed over the gate dielectric layer110/114. The gate electrode layer preferably comprises a semiconductormaterial, such as polysilicon or amorphous silicon, althoughalternatively, other semiconductor materials may be used for the gateelectrode layer 112/116. In other embodiments, the gate electrode layer112/116 may comprise TiN, HfN, TaN, W, Al, Ru, RuTa, TaSiN, NiSi_(x),CoSi_(x), TiSi_(x), Ir, Y, Pt, Ti, PtTi, Pd, Re, Rh, borides,phosphides, or antimonides of Ti, Hf, Zr, TiAlN, Mo, MoN, ZrSiN, ZrN,HfN, HfSiN, WN, Ni, Pr, VN, TiW, and/or combinations thereof, asexamples.

In preferred embodiments, the NVM gate stack is patterned and etchedusing a hard mask technique with the dedicated NVM gate mask, althoughin other embodiments resist soft mask or other masking materials can beused. This patterning is shown in step 172, wherein tetraethyloxysilane(TEOS) gas is used as a precursor gas to form an anti-reflective coatinglayer of SiO₂ on the wafer. In other embodiments, the hard mask layercould consist of other materials such as Si_(x)N_(y), for example.

The NVM gate stacks are etched in step 176. In some embodiments, thelayer of photoresist is patterned using the lithography mask, and thenthe layer photoresist is used to pattern the hard mask. The layer ofphotoresist may then be removed, and the hard mask is used to patternthe material layer, for example. Or, alternatively, both the layer ofphotoresist and the hard mask are used to pattern the material layer. Inpreferred embodiments, the hard mask may be left remaining, or it may beremoved. In the preferred embodiment the NVM gate stack is etched usingan RIE.

In step 178, the NVM source/drain is doped. In a preferred embodiment,doping is done though an ion implant process where arsenic or phosphorusions are implanted. In the preferred embodiment, the NVM devices aren-channel devices, so the source/drain will be implanted with an n-typematerial. In other embodiments, where a p-channel NVM is formed, thesource/drain regions are doped with p-type material such as boron. Inone embodiment, phosphorus ions can be implanted with a dose of about5×10¹³ cm⁻² to about 5×10¹⁴ cm⁻² and an implant energy between about 20keV and about 80 keV. In step 179, the TEOS Hard Mask is removed.

In step 180, the NVM device source/drain is then annealed to repair anyimplantation damage. In a preferred embodiment, a high temperatureanneal is performed for about 30 minutes at a temperature of about 900°C., forming about 15 nm sidewall oxidation.

In step 182, the gates of the standard logic are patterned and etchedusing standard techniques. Either a hard mask or a soft mask can beused. In a preferred embodiment of the present invention, photoresistand an RIE are used to etch the standard logic gates.

Because of damage to the standard logic device's polysilicon gates,first spacers 120 are formed in step 184, which includes a re-oxidationstep to encapsulate the polysilicon gate and a low temperature oxide(LTO) is deposited on the sidewalls of the gate stack LV, HV and overthe extension areas of the NVM device. In a preferred embodiment, afurnace thermal oxidation (e.g., 900° C., 10 min.) is used to accomplishthis, although the first spacers 120 may alternatively comprise anitride.

In step 186, the LDD extension regions for the high voltage devices areimplanted using HV masks. In step 190 the LV extension and halo regionsare formed for the standard logic devices.

Second spacers 122 are formed over the first spacers 120 in step 191. Ina preferred embodiment, the second spacers typically comprise a nitridesuch as silicon nitride. Alternatively the second spacers may be madefrom an oxide.

The source/drain regions of the standard devices 102, HV as well as theNVM 100 devices are implanted in step 192. If a p-type transistor is tobe formed, a p-type ion implant is used to form the heavily doped sourceand drain regions. For example, boron ions can be implanted with a doseof about 5×10¹⁴ cm⁻² to about 5×10¹⁵ cm⁻² and an implant energy betweenabout 10 keV and about 50 keV. In other embodiments, other materials,such as BF₂ or In, can be implanted. If an n-type transistor is to beformed, an n-type ion implant is used to form the heavily doped sourceand drain regions. In the preferred embodiment, arsenic or phosphorusions are implanted into the source/drain regions. For example, arsenicions can be implanted with a dose of about 5×10¹⁴ cm⁻² to about 5×10¹⁵cm⁻² and an implant energy between about 30 keV and about 80 keV. Inother embodiments, other materials, such as Sb, can be implanted.

Silicide regions 118 are formed over the control gate 112 and oversource/drain contact areas to form low resistivity upper surface regionsin step 194. Silicide is formed by first depositing a silicidation metalover the semiconductor body 104, the control gate 112, and over the gateelectrode 116, then subjecting the structure to an annealing process. Inthe preferred embodiment, the silicidation metal is nickel, but themetal could also be cobalt, copper, molybdenum, titanium, tantalum,tungsten, erbium, zirconium, platinum, or combinations thereof. In oneexample, the semiconductor body 104 is then heated to about 400° C. or500° C. to form a single layer of nickel silicide.

In the first embodiment of the present invention, as shown in FIG. 1 b,and as described in the process flow chart of FIG. 1 e, a stressproximity technique (SPT) is used to increase the stress impact to thegate dielectric from the contact nitride liner in order to reducetunneling leakage. Second spacer 122, is removed from devices 100 and102 in step 195. In the first embodiment of the present invention,removal is achieved by an isotropic RIE, although other methods, such asa wet etch, may alternatively be used.

Turning to FIG. 1 c, a stress inducing liner 124 is deposited overdevices 100 and 102. In one embodiment, dual stress liners (DSL) areused, as indicated by step 197. The stress liner 124 is typically formedby deposition of a nitride layer with a tensile or compressive stress.For example, a nitride film (e.g., silicon nitride) can be deposited insuch a way as to create a stress between the stress liner 124 and theunderlying gate stack. For a silicon nitride liner, typically the Si—Nto Si—H bonding influences the stress direction—the lower Si—H to Si—Nratio, the more tensile. As is known in the art, deposition rate,pressure, UV curing, and other factors dictate this ratio.

The applied stress-inducing liners are tensile for the n-channeltransistor devices 102 and compressive for p-channel transistor devices102 (either standard or high voltage devices). Alternatively in otherembodiments, only a tensile liner may be formed on the n-channel deviceswith no liner being formed on the p-channel devices, or only acompressive liner may be formed on the p-channel devices and no liner isformed on the standard and high voltage n-channel devices.

The NVM device 100 also receives stress from the stress liner. In thepreferred embodiment, this stress will change the band gap of the gatestack 106. For an n-channel NVM (i.e., where the source/drain regionsare n-doped), a tensile strained liner 124 is preferably used.

Referring now to FIG. 1 d, the additional processing sequence of step198 is illustrated. An interlayer dielectric (ILD) layer 128 is formedover the stress liner 124 which serves as an etch stop layer. SuitableILD layers include materials such as SACVD oxide, plasma enhancedtetraethyloxysilane (TEOS), doped glass (BPSG, PSG, BSG), organosilicate glass (OSG), fluorinated silicate glass (FSG), andspin-on-glass (SOG), as examples. Typically, the gate electrode (notshown) and source/drain contacts 126 are formed through the interlayerdielectric. Metallization layers that interconnect the variouscomponents are also included in the chip, but not illustrated for thepurpose of simplicity.

In the second embodiment of the present invention, the cross-sections ofwhich are shown in FIGS. 2 a-2 c, and described in the process flowchartof FIG. 2 d. Unlike the SPT technique of the first embodiment processdescribed herein above, the second embodiment process uses a stressmemory technique (SMT) to stress the flash gate stack. In the secondembodiment, processing proceeds similarly to the first embodiment up tothe standard logic source/drain implant step 192.

Referring to FIG. 2 a and the process flow chart of FIG. 2 d,semiconductor body 104 is shown on top of which an NVM device isfabricated just prior to SMT step 193. As is described above, a tunneloxide layer 106, a floating gate 108, an insulating layer 110, and acontrol gate 112 are formed over the semiconductor body 104. A firstspacer 120 is formed on the sidewalls and extension area of the NVMdevice and on the sidewalls and extension areas of the standard device.A second spacer 122 is formed on the first spacer.

Turning to FIG. 2 b, a stress liner 130 is deposited on device 100. Asbefore, a tensile or compressive stressed liner can be deposited. Forexample a tensile nitride is preferably deposited using PECVD, althoughalternatively other deposition techniques can be used. The memory deviceis typically an n-channel device that includes a tensile strained liner.

After the stress liner is deposited on device 100, a spike annealingstep is performed wherein the semiconductor body is heated to atemperature between 900° C. and 1200° C., preferably about 1100° C. Thespike anneal crystallizes the semiconductor of gate 112 in a manner thatcauses the strain to remain (“be memorized”) within the material. Afterthe annealing step, the stress liner is removed, e.g., using a wet etchas shown in FIG. 2 c. The etch stops at the dielectric layer 120.Alternatively, other techniques such as RIE can be used to remove thestress liner.

The source/drain regions (not shown) and the control gate 112 aresilicided as described above herein in step 194. Processing continueswith the application of dual stress liners in step 197 and ILD andcontact formation in step 198 as shown in FIG. 2 d and described hereinabove.

A third embodiment of the present invention is described in thecross-sectional views of FIGS. 3 a-3 c, and in the process flowchart ofFIG. 3 d. In this embodiment, an SMT technique is also used. The stressliner is deposited earlier in the process after the floating gate isetched in step 160 and after a first spacer is deposited on thepartially fabricated NVM gate stack in step 161.

Referring to FIG. 3 a, semiconductor body 104 is shown, on top of whichan NVM device is fabricated. As is described herein above, a tunneloxide layer 106 and a floating gate 108, are formed over thesemiconductor body 104. A first spacer 120 is formed on the sidewallsand extension area of the NVM device in step 161 of the processflowchart of FIG. 3 d.

Turning to FIG. 3 b, a stress liner 140 is deposited on device 100. Inthe third embodiment of the present invention, where an n-channel NVMtransistor is to be formed, the stress liner 140 is typically a tensilestress nitride deposition. The deposition is preferably deposited usingPECVD, although alternatively, RTCVD can be used. In other embodimentswhere p-channel transistors are formed, a compressive stress liner istypically used.

The gate 108 is typically polycrystalline prior to deposition of thestress liner 140. In another embodiment, the gate layer 108 is depositedas amorphous silicon.

After the stress liner is deposited on device 100, a spike annealingstep is performed wherein the semiconductor body is heated to atemperature between 900° C. and 1200° C., preferably about 1100° C. Thespike anneal causes the stress imparted in the gate 108 (and possiblythe exposed semiconductor body 104) to be retained in the crystallizedsemiconductor. After the annealing step, the stress liner is removedusing a wet etch.

Processing continues according to the process flowchart of FIG. 3 d andas described herein above beginning with the ONO dielectric formation ofstep 163.

It will also be readily understood by those skilled in the art thatmaterials and methods may be varied while remaining within the scope ofthe present invention. It is also appreciated that the present inventionprovides many applicable inventive concepts other than the specificcontexts used to illustrate preferred embodiments. Accordingly, theappended claims are intended to include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or steps.

1. A method of making a semiconductor device, the method comprising:forming a gate dielectric over a semiconductor body: forming a floatinggate over the gate dielectric; forming an insulating region over thefloating gate; forming a control gate over the insulating region;forming a stress inducing liner over the floating gate: annealing a gatematerial underlying and physically contacting the stress inducing liner,thereby memorizing stress in the gate material; and removing the stressinducing liner.
 2. The method of claim 1, further comprising amorphizingthe control gate prior to forming the stress inducing liner.
 3. Themethod of claim 1, wherein forming the control gate comprisessimultaneously forming a gate for a logic transistor.
 4. The method ofclaim 3, further comprising inducing a stress in the gate dielectric andin the logic transistor.
 5. The method of claim 1, wherein annealing thegate material comprises performing a spike anneal.
 6. The method ofclaim 1, wherein the stress inducing liner is removed using a wet etch.7. The method of claim 1, wherein the stress inducing liner comprises anitride liner.
 8. The method of claim 1, wherein the gate dielectriccomprises a stressed gate dielectric having an energy gap that isgreater than a band gap of a relaxed gate dielectric having a samematerial as the stressed gate dielectric.
 9. The method of claim 4,wherein the logic transistor includes a compressively strained channel.10. The method of claim 4, wherein the logic transistor includes atensilely strained channel.
 11. The method of claim 1, wherein the gatematerial is the control gate, and wherein, forming the stress inducingliner, annealing the gate material, and removing the stress inducingliner are performed after forming the control gate.